Preparation techniques and mechanisms of formation of biodegradable nanoparticles from preformed polymers

The techniques available to prepare biodegradable nanoparticles (nanospheres and nanocapsules) from preformed polymers are reviewed. Although there is abundant literature on this topic, only a few focus on the thorough analysis of preparative procedures. In particular, four techniques are discussed in terms of their technological advantages and drawbacks: emulsification evaporation, solvent displacement, salting-out, and emulsification diffusion. The proposed mechanism of nanoparticle formation for each technique is described from a physicochemical perspective. The effects of preparative variables on nanoparticle size and drug-entrapment efficiency are also discussed.